1. Field of the Invention
This invention relates to a focus detecting device for forming optical images of substantially the same object on a pair of photoelectric element arrays by two light beams passed through two different areas of the exit pupil of an imaging optical system such as a photo-taking lens and effecting focus detection from the relative image displacement amount of the two optical images.
2. Description of the Prior Art
Focus detecting devices of this kind have been adopted in single lens reflex cameras, video cameras, etc., and generally the following two types of such devices are known. The first type is a system in which, as shown in U.S. Pat. No. 4,264,810, primary images of an object formed by a photo-taking lens are re-imaged on a pair of photoelectric element arrays by a pair of re-imaging optical system, and the second type is a system in which, as described in U.S. Pat. No. 4,185,191, a row of minute lenses are disposed substantially on the focal plane of a photo-taking lens and a pair of photoelectric elements are provided behind each of the minute lenses.
Such focus detecting devices suffer from a disadvantage that if a pair of light beams used for focus detection, i.e., light beams forming optical images on the pair of photoelectric element arrays, are vignetted by the aperture or the like of the photo-taking lens, the focus detecting accuracy will be reduced greatly.